The invention relates to electrically controlled fuel injection systems for internal combustion engines. More particularly, it relates to fuel injection systems in which injection pulses are generated from information which is obtained in synchronism with crankshaft rotations. The duration of the injection pulses is derived from particular operating conditions of the engine and includes several partial circuits which generates crankshaft-synchronous output pulses which relate to engine parameters and which are fed to logical circuits which alter the pulse durations. The system also includes an air flow rate meter which generates an appropriate signal which is used in the generation of the fuel control pulses.
The known electrical or electronically controlled fuel injection systems have progressed, primarily to reduce cost, from individual injection for each cylinder to the process of simultaneously injecting fuel into all cylinders or induction tubes of the engine, which is now the prevailing practice. In order to improve transient behavior of the engine, it has also been proposed to divide the fuel required by each operating cycle of the engine and to deliver it in two separate injection events. However, even such a division still is incapable of coping with a very rapidly changing air flow rate occurring during a sudden acceleration of the engine. Since fuel is delivered at exact predetermined times, and the quantity of fuel relates to the air flow then occurring, the engine may not receive the proper amount of fuel when the air flow rate changes very rapidly. Thus, in the case of very abrupt accelerations or changes of the aspirated air quantity, the engine torque decreases and it loses power, the driving sensations deteriorate and, if the fuel starvation becomes large enough, it may lead to engine misfires and to a considerable deterioration of the exhaust gas composition. In order to counteract such disadvantages when simultaneous injection to all cylinders is employed,it is possible to shift the point of injection to the time when the rapid change occurs and to feed an amount of fuel to the engine which is based on a fixed pulse width. However, this also invites difficulties because both the amount of fuel as well as the timing of the injection point can be in error and thus the correct amount of fuel may not be fed to the engine at the right time. Thus, if the fuel fed to the engine is not delivered at the exact time of the sudden change in the air flow rate, it may actually be too large for the required conditions which again deteriorates the exhaust gas composition and diminishes the driving comfort. Thus, in a known system, if the acceleration injection signals are associated with the instant at which a throttle valve exceeds a certain opening position, and if the injection takes place at that time, any further acceleration or displacement of the throttle valve would have no effect. It has also been found in tests that, after a rapid change of the aspirated air quantity if fuel is injected at the moment the throttle valve has obtained its maximum opening there may be a considerable deterioration in the engine behavior and in the fuel-air composition. This tendency to deteriorate the engine behavior is especially great in known fuel injection systems if, for example during a gear change, the engine is taken very rapidly from deceleration to acceleration and, more especially, if the system includes a throttle valve damper or a similar mechanism so as to eliminate delaying effects.